Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$88.51	13.862%	$100.7793	$100.78	$100.80	$100.80
Purchase #2	$221.59	7.180%	$237.5002	$237.50	$237.50	$237.50
Purchase #3	$11.66	12.252%	$13.0886	$13.09	$13.10	$13.10
Purchase #4	$244.68	5.844%	$258.9791	$258.98	$259.00	$259.00
Purchase #5	$250.33	5.797%	$264.8416	$264.84	$264.85	$264.80
Purchase #6	$49.69	12.788%	$56.0444	$56.04	$56.05	$56.00
Purchase #7	$161.60	4.175%	$168.3468	$168.35	$168.35	$168.30
7 purchase totals =	$1,028.06		$1,099.5800	$1,099.58	$1,099.65	$1,099.50